Presently, there are two kinds of conventional speed-control systems for a DC elevator, one of which is a generator-motor speed-control system excited with a silicon controlled rectifier (SCR), another is a SCR-motor speed-control system powered directly by a SCR. The elevator with the former speed-control system has some drawbacks, such as higher exhausted energy, larger room occupied by the elevator, higher noise, lower response speed and higher cost. The latter speed-control system has higher pulsating current and higher ripple torque, and its current is intermittent when the speed of elevator is low, because it is directly powered with the regulated voltage by SCR from an AC power supply. It is difficult to satisfy a passenger's comfort requirements so that its application to an elevator is limited. Furthermore, there are other drawbacks e.g., it has a lower power factor and needs larger-volume smoothing inductors and loop reactors etc.